Missing” heat may affect future climate change

2010-10 FOR IMMEDIATE RELEASE: April 15, 2010

“Missing” heat may affect future climate change

Contacts:

David Hosansky, NCAR/UCAR Media Relations
303-497-8611
hosansky@ucar.edu

Rachael Drummond, NCAR/UCAR Media Relations
303-497-8604
rachaeld@ucar.edu

BOULDER--Current observational tools cannot account for roughly half of
the heat that is believed to have built up on Earth in recent years,
according to a “Perspectives” article in this week’s issue of Science.
Scientists at the National Center for Atmospheric Research (NCAR) warn
in the new study that satellite sensors, ocean floats, and other
instruments are inadequate to track this “missing” heat, which may be
building up in the deep oceans or elsewhere in the climate system.

“The heat will come back to haunt us sooner or later,” says NCAR
scientist Kevin Trenberth, the lead author. “The reprieve we’ve had from
warming temperatures in the last few years will not continue. It is
critical to track the build-up of energy in our climate system so we can
understand what is happening and predict our future climate.”

The authors suggest that last year’s rapid onset of El Niño, the
periodic event in which upper ocean waters across much of the tropical
Pacific Ocean become significantly warmer, may be one way in which the
solar energy has reappeared.

The research was funded by the National Science Foundation, NCAR’s
sponsor, and by NASA. A Science Perspectives piece is not formally
peer-reviewed, but it is extensively reviewed by editors of the journal.
Science had invited Trenberth to submit the article after an editor
heard him discuss the research at a scientific conference.

Trenberth and his co-author, NCAR scientist John Fasullo, focused on a
central mystery of climate change. Whereas satellite instruments
indicate that greenhouse gases are continuing to trap more solar energy,
or heat, scientists since 2003 have been unable to determine where much
of that heat is going.

Either the satellite observations are incorrect, says Trenberth, or,
more likely, large amounts of heat are penetrating to regions that are
not adequately measured, such as the deepest parts of the oceans.
Compounding the problem, Earth’s surface temperatures have largely
leveled off in recent years. Yet melting glaciers and Arctic sea ice,
along with rising sea levels, indicate that heat is continuing to have
profound effects on the planet.

Trenberth alluded to this mystery in a widely misconstrued e-mail in
which he wrote, “The fact is that we can’t account for the lack of
warming at the moment and it is a travesty that we can’t.” That message
was one of thousands of e-mails and other documents obtained without
authorization last year from the University of East Anglia’s Climatic
Research Unit and disseminated on the Web.

In their Perspectives article, Trenberth and Fasullo explain that it is
imperative to better measure the flow of energy through Earth’s climate
system. For example, any geoengineering plan to artificially alter the
world’s climate to counter global warming could have inadvertent
consequences, which may be difficult to analyze unless scientists can
track heat around the globe. Improved analysis of energy in the
atmosphere and oceans can also help researchers better understand and
possibly even anticipate unusual weather patterns, such as the cold
outbreaks across much of the United States, Europe, and Asia over the
past winter.

-----There’s more to climate change than warmer air-----

As greenhouse gases accumulate in the atmosphere, satellite instruments
show a growing imbalance between energy entering the atmosphere from the
Sun and energy leaving from Earth’s surface. This imbalance is the
source of long-term global warming.

But tracking the growing amount of heat on Earth is far more complicated
than measuring temperatures at the planet’s surface. The oceans absorb
about 90 percent of the solar energy that is trapped by greenhouse
gases. Additional amounts of heat go toward melting glaciers and sea
ice, as well as warming the land and parts of the atmosphere. Only a
tiny fraction warms the air at the planet’s surface.

Satellite measurements indicate that the amount of greenhouse-trapped
solar energy has risen over recent years while the increase in heat
measured in the top 3,000 feet of the ocean has stalled. Although it is
difficult to quantify the amount of solar energy with precision,
Trenberth and Fasullo estimate that, based on satellite data, the amount
of energy build-up appears to be about 1.0 watts per square meter or
higher, while ocean instruments indicate a build-up of about 0.5 watts
per square meter. That means about half the total amount of heat is
unaccounted for.

A percentage of the missing heat could be illusory, the result of
imprecise measurements by satellites and surface sensors or incorrect
processing of data from those sensors, the authors say. Until 2003, the
measured heat increase was consistent with computer model expectations.
But a new set of ocean monitors since then has shown a steady decrease
in the rate of oceanic heating, even as the satellite-measured imbalance
between incoming and outgoing energy continues to grow.

Some of the missing heat appears to be going into the observed melting
of ice sheets in Greenland and Antarctica, as well as Arctic sea ice,
the authors say.

Much of the missing heat may be in the ocean. Some heat increase can be
detected between depths of 3,000 and 6,500 feet (about 1,000 to 2,000
meters), but more heat may be deeper still beyond the reach of ocean
sensors.

Trenberth and Fasullo call for additional ocean sensors, along with more
systematic data analysis and new approaches to calibrating satellite
instruments, to help resolve the mystery. The Argo profiling floats that
researchers began deploying in 2000 to measure ocean temperatures, for
example, are separated by about 185 miles (300 kilometers) and take
readings only about once every 10 days from a depth of about 6,500 feet
(2,000 meters) up to the surface. Plans are underway to have a subset of
these floats go to greater depths.

“Global warming at its heart is driven by an imbalance of energy: more
solar energy is entering the atmosphere than leaving it,” Fasullo says.
“Our concern is that we aren’t able to entirely monitor or understand
the imbalance. This reveals a glaring hole in our ability to observe the
build-up of heat in our climate system.”

The University Corporation for Atmospheric Research manages the National
Center for Atmospheric Research under sponsorship by the National
Science Foundation. Any opinions, findings and conclusions, or
recommendations expressed in this publication are those of the author(s)
and do not necessarily reflect the views of the National Science Foundation.

-The End-

Title
“Tracking Earth’s Energy”

Authors
Kevin Trenberth and John Fasullo

Publication
Science, April 16, 2010

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